1. Field of the Invention
This invention relates to mobile radio communication apparatuses such as mobile telephones, portable telephones and cordless telephones, and more particularly to a dual mode mobile radio communication apparatus to be used as a mobile unit in a mobile radio communication system, which performs radio transmission of communication signals by selectively using analog and digital modes between a base station and the mobile unit.
2. Description of the Related Art
Recently, a dual mode system has been used in place of a conventional mobile radio communication system for performing radio transmission of communication signals of analog mode. Here, the "dual mode system" means a system which employs analog mode and digital mode.
In the analog mode system, a carrier wave is frequency-modulated in accordance with an analog voice signal and data in a transmission device, and the modulated wave is transmitted to a receiving device where the modulated wave is demodulated to thereby reproduce the analog voice signal and data. On the other hand, in the digital mode system, a voice signal and data are encoded in a transmission device, and carrier wave is subjected to digital modulation in accordance with the encoded signal and data by use of a .pi./4 shifted DQPSK (Differentially encoded Quadrature Phase Shift Keying) method. The modulated wave is transmitted from the transmission device to a receiving device, where the modulated wave is subjected to digital demodulation, and then the demodulated signal and data are decoded to thereby reproduce the voice signal and data.
In recent years, it has been proposed to employ a remote control function in a mobile radio communication apparatus for use in the above-described systems. This remote control function is means to perform remote control of a destination terminal with use of remote control data by transmitting the remote control data from the mobile radio communication apparatus to the destination terminal through a communication link established therebetween. This function is very convenient since it enables the user to reproduce and hear a message stored in a destination terminal (if the terminal is an answering telephone), or to contact a destination terminal so as to make, for example, ticket reservations from a remote place (if the terminal is dedicated to ticket reservation).
In the above-described dual mode mobile radio communication apparatus, however, the manner of transmission of remote control data differs depending upon whether the communication mode is analog mode or digital mode. The remote control data consists of a DTMF signal in the analog mode, whereas it consists of a message code in the digital mode. From the message code transmitted in the digital mode, the user cannot check whether or not he has performed correct operation and whether he has transmitted correct data, although he can check when the DTMF signal is transmitted in the analog mode.